#9 -v CLI flag for querying the installed Checkstyle version

src/main/java/com/puppycrawl/tools/checkstyle/Main.java

@@ -56,6 +56,7 @@ public final class Main
             "f",
             true,
             "Sets the output format. (plain|xml). Defaults to plain");
+        OPTS.addOption("v", false, "Print product version and exit");
     }
 
     /** Stop instances being created. */
@@ -82,6 +83,12 @@ public final class Main
         }
         assert line != null;
 
+        // show version and exit
+        if (line.hasOption("v")) {
+            System.out.println("Checkstyle version: " + Main.class.getPackage().getImplementationVersion());
+            System.exit(0);
+        }
+
         // setup the properties
         final Properties props =
             line.hasOption("p")